共查询到19条相似文献,搜索用时 62 毫秒
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竖直平面上的传热传质复合自然对流 总被引:3,自引:0,他引:3
用数值方法研究了竖直平面上因热及物质扩散引起的传热传质复合自然对流,得到了速度、压力、温度和浓度的分布及传热传质速率随浮力比的变化规律。研究结果表明:Nu与Sh在随浮力比B的变化过程中出现最小值,此时的浮力比Bmin仅是Pr/Sc的函数;流型取决于浮力比和Pr/Sc,根据流型不同可在B-Pr/Sc坐标系中将流场划为4个区域。 相似文献
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超临界压力下水在倾斜管内传热特性的研究 总被引:4,自引:0,他引:4
以水为工质,在倾角α=14°和10°、压力22.0~28.OMPa、质量流速600~1400kg/(m~2·s)、内壁热负荷250~410kW/m~2的参数范围内,研究了水(特别是在大比热区附近)的传热特性.针对微倾斜管中,内壁面既非定壁温也非定热流的边界条件下,成功地提出了二维温度场计算方法,从而获得了传热系数、努赛尔特数等.分别在传热恶化前及传热恶化后两个区域内关联了传热系数数据.对于超临界流体在最大比热区附近呈现的特殊传热特性规律进行了分析,并研究了倾斜管中由于浮升力引起的自然对流对各参数沿周向分布的影响. 相似文献
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垂直梯度磁场作用下水平薄层磁性液体自然对流传热 总被引:5,自引:0,他引:5
1前言磁性液体是吸附着表面活性剂的固体磁性颗粒(如Fe3O4)分散于基液(如水)中而形成的稳态胶体溶液。它能在重力、磁力及离心力等外力场的作用下不凝聚、不沉淀,是一种集流动性。强磁性于一体的新型材料。磁性液体在化工、机械、电子、动力及航天航空等领域有... 相似文献
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文章通过自然对流传热系数主要影响因素的因次分析过程,论述了因次分析方法在化工理论计算式推导中的普遍意义。 相似文献
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在重力场中流体密度变化产生自然对流,在磁力场中磁性液体的表观密度随外加磁场强度的变化而明显变化,磁场可以改变磁性液体的自然对流.通过对磁场中的磁性液体的静力学计算和分析,建立一个由均匀磁场和均匀梯度磁场同轴叠加的合成磁场,合成磁场使磁场引起的磁性液体密度变化各处均等,各处的自然对流传热均等,从而使磁性液体的表观密度和自然对流传热系数得以准确测量,由此建立起磁性液体的磁场强度、表观密度、Grashof数之间的关联式.磁场强度的增大使磁性液体表观密度增大,使磁性液体处于超重状态,是磁场强化磁性液体自然对流传热的机理. 相似文献
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人工合成的潜热型功能性热流体同时具有流动性与高的蓄热或蓄冷能力,在自然对流的流动与传热中表现有复杂的非线性传热和流动现象。本文总结了该类流体在自然对流传热方面的最新研究进展,包括:自然对流的强化传热及其稳定性,乳液中微粒的粒径及其乳液热物性的影响,对该方面将来的发展趋势进行了展望。 相似文献
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In this article, we apply the differential transform method (DTM) to obtain approximate analytical solutions of combined free and forced (mixed) convection about inclined surfaces (or wedges) in a saturated porous medium. Both aiding and opposing flows are considered. It is found that the parameter mixed convection from inclined surfaces in porous media is Gr/Re, where Gr is the local Grashof number and Re is the local Reynolds number. DTM solutions are obtained for mixed convection from an isothermal vertical flat plate as well as an inclined plate with constant heat flux having an inclination of 45°. Temperature and velocity profiles for these two cases at different values of Gr/Re are presented. The similarity transformations are applied to reduce the governing partial differential equations (PDEs) to a set of nonlinear coupled ordinary differential equations (ODEs) in dimensionless form. DTM is used to solve the nonlinear differential equations governing the problem in the form of series with easily computable terms. Thereafter a Padé approximant is applied to the solutions to increase the convergence of the given series. Excellent correlation between DTM-Padé and numerical quadrature (shooting) solutions is achieved. The DTM-Padé simulation is shown to be a robust benchmarking tool providing an excellent means of validation of numerical methods. The study has applications in geothermal energy systems, chemical engineering filtration systems, and packed beds. 相似文献
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Rama Subba Reddy Gorla 《Chemical Engineering Communications》1986,49(1):13-22
An analysis is presented to study the effects of buoyancy-induced streamwise pressure gradients on laminar forced convection heat transfer to non-Newtonian fluids from a horizontal plate. Numerical solution of the transformed boundary layer equations has been carried out for different values of the flow behavior index and the buoyancy parameter by means of the local nonsimilarity method. A discussion is provided for the effect of the buoyancy force on the friction factor, the dimensionless heat transfer rate and the details of the velocity as well as temperature fields. 相似文献
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Available boundary layer type solutions to the combined hydrodynamic and thermal entrance region problem are known to exhibit a discontinuity in the gradients of the velocity and temperature distributions in the entrance region. A new solution is presented which alleviates this shortcoming. The new solution is based on the hydrodynamic inlet-filled region concept originally proposed by Ishizawa (1966) and later adopted by Mohanty and Das (1982) to hydrodynamically developing flow in a channel. This concept is extended to the combined entry length problem by dividing the thermal entrance length into two lengthwise regions, a thermal inlet region and a thermally filled region. In the former, the effect of heat transfer between fluid and wall is confined within the thermal boundary layer developing along the wall. At the end of the thermal inlet region, the thermal boundary layers meet at the duct axis but the temperature profile is not yet developed. In the thermally filled region, the heat effects propagate throughout the entire cross section and the temperature profile undergoes adjustment in a fully thermal region to finally attain the fully developed form. A thermal shape factor is also introduced in the thermally filled region which ensures that all thermal quantities attain their fully developed values asymptotically. The new model is used to obtain solutions to the combined entry length problem for laminar flow through a parallel plate channel under the constant wall heat flux boundary condition. The analysis gives considerably better results for the local Nusselt number and thermal entrance length than previously available. 相似文献
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The developing flow and heat transfer in the entry region of a heated circular tube is analyzed for the case of constant wall temperature. An integral or boundary-layer solution is presented which has a number of advantages over earlier Karman-Pohlhausen integral analyses. Thus, in the present analysis, the velocity and temperature distributions, the local and mean drag coefficients, and the local and mean Nusselt numbers approach their fully-developed values asymptotically. The new analysis is based on the hydrodynamic inlet-filled region concept originally proposed by Ishizawa (1966) and later adopted by Mohanty and Asthana (1978) to flow through a circular tube. This concept is extended to the combined entry-length problem by introducing a thermal transition region, herein called the thermally-filled region, between the thermal inlet boundary-layer region and the thermally fully-developed region. A thermal shape factor is also introduced which ensures smooth transition of all pertinent thermal quantities from the entrance region to the fully-developed region. Results for the variation of the local and mean Nusselt numbers with axial distance along the tube for Pr = 0.1,0.5,0.7,1,5, and 10 are presented. These results agree well with the numerical solutions of Hombeck (1965), Manohar (1969), and Hwang and Sheu (1974) and also with the correlations of Churchill and Ozoe (1973). 相似文献
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离心流化床中强制对流换热的实验研究 总被引:1,自引:0,他引:1
对离心流化床干燥器中气体与被干燥颗粒物料之间的强制对流换热进行了实验研究,获得了各主要运行参数对气固换热系数的影响规律,并利用场协同原理分析了对流换热强化的机理. 实验证明,在一定转速范围内,在气流速度方向和热流方向(温度梯度方向)一致时,换热的准则关联式具有Nu=CRePr的形式. 获得了满足Nu~RePr呈直线关系的Pe(Pe=RePr)数变化范围和临界Pe数,当Pe数大于临界值后,离心流化床中对流换热强度随Pe数增加而增大的趋势会明显减缓并偏离线性区. 相似文献
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用实验和数值两种方法研究了倾斜密闭容器中半透过性流体在辐射光的照射下产生的自然对流现象及其对传热的影响.首先建立了基于二维假设下的流体流动和热量传递的动态数学模型,并用有限差分方向交替法进行数值求解,得到稳态下的等温线和流线图.结果表明,流体的自然对流和传热受光学厚度和容器倾斜角度的影响.还建立了实验装置,测量了稳态下的温度分布.理论计算与实验结果比较表明两者的变化趋势一致,吻合较好. 相似文献
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In an inclined-vibrated fluidized bed (IVF-bed), solid particles are fluidized easily at a relatively low air velocity. Good mixing of the fluidized particles in the direction of the air flow and the renewal of the bed surface take place as a result of the vibration effect. Accordingly when the bed surface is heated by thermal radiation from the top surface, radiant heat is absorbed more effectively on the surface than on a stagnant bed surface. This characteristic of an IVF-bed indicates the applicability to a solar dryer and other similar dryers. The present study reports the result of model experiments carried out to confirm the effectiveness of radiative heating on drying of wet granular materials. Further, for quantitative evaluation of the radiation effect, a theoretical model is offered and its validity is examined. 相似文献